Topological crystalline insulators (TCIs) are a new class of materials that exhibit an insulating bulk yet possess conducting states at the surface. The metallic character of the surface states relies on having a crystal symmetry (e.g. mirror symmetry) that prevents the surface from becoming insulating. In this collaborative theoretical study (with the group of Liang Fu, at MIT), it has been demonstrated that a small electric field can break this symmetry and turn the surface states into an insulating state. Since this electric field can be externally controlled, the device effectively works as a topological insulator transistor switch. This enables the charge and spin transport at the surface of TCIs to be controlled with high on/off ratio, fast operational speed and low energy consumption. This new approach may lead to the development of TCI based electronic and spintronic technology beyond the current CMOS technology.